Method for processing biomass

ABSTRACT

The invention relates to a method for processing biomass, such as in particular green waste containing wood, and a high density pulper having a spiral, wherein the green waste is treated in a continuously operated, bladed pulper and then the separated fibers are ground in a pulper ball mill.

The invention relates to a method for preparing biomass, such as in particular wood-containing green waste, and a high-consistency pulper having a spiral.

A specific method is required in particular for processing biomass in pulpers for producing cellulose and wood pulp fibres for paper production, as the biomass must be processed thoroughly in order to release the cellulose fibres and the process must be conducted in such a manner that cellulose fibre lengths which are suitable for paper production are obtained.

The invention is therefore based on the object of providing a method for preparing biomass, with which fibres of specific length and properties, in particular for paper production, can be obtained.

This object is achieved with a method for preparing biomass, such as in particular wood-containing green waste, in which the biomass is treated in a continuously operated, bladed pulper and then the separated fibres are milled in a pulper ball mill.

The specific combination of bladed pulper with the treatment in a pulper ball mill surprisingly led to a method with which biomass can be treated in a particularly simple manner to provide fibres. Fibres can therefore be provided for a variety of uses depending on the treatment step and configuration of the bladed pulper and of the balls for the ball mill.

It is advantageous if the bladed pulper is operated as a high-consistency pulper. An advantageous consistency in the bladed pulper is therefore from 10 to 20% dry content.

The speed of the blade relative to the biomass is of great relevance. Particularly good results have been achieved with blade speeds of over 10 m/sec relative to the biomass.

It is ideal for use of the fibres in the paper industry if the separated fibres have a length between 1 mm and 5 mm.

It is advantageous, in particular if the biomass has a high content of woody constituents, if the biomass is processed dry before treatment in the continuously operated bladed pulper. To this end, a rapidly rotating blade, such as in a lawnmower, can be used with subsequent dry screening in addition to feedback of the oversize material. This means that a classical mill/classifier system is used and, for example, the biomass produced is separated in the form of for example wood chips and for example fed to a biomass combined heat and power plant.

It is advantageous, in particular if the biomass has wood constituents, if the biomass is heated before treatment in the continuously operated bladed pulper. This also makes it possible to treat wood waste, green waste with wood-containing parts and even comminuted wood and wood chips.

To ensure that water penetrates into the wood or wood-containing constituents, it is proposed that the biomass be heated under pressure. An autoclave can be used for this. Continuous heaters can however also be used. In the process, water can be supplied and steam can be let out in order to influence the processes during heating.

It is advantageous if the biomass is kept hot for several hours. If no steam is let out, it is sufficient to bring the biomass preferably under pressure to a temperature of for example between 100° C. and 200° C., so that the biomass becomes soft and thereby easier to handle.

It is proposed in particular for the wood pulp milling that the separated cellulose fibres be concentrated on a screening machine and freed from fine material which impedes the milling process after it has been treated in the continuously operated bladed pulper.

Particularly good results are achieved by milling the separated fibres in the pulper ball mill in a fibrillating manner.

To treat the separated fibres it is proposed that these fibres be milled in the pulper ball mill with lightweight balls which have approximately the density of plastic. The separated fibres are thus subjected to careful treatment in a pulper ball mill as undersize material.

It is furthermore advantageous if the oversize material of the continuously operated bladed pulper is milled in a pulper ball mill with heavy balls which have approximately the density of steel, stone or ceramic.

Depending on the result, it can be advantageous if post-sorting takes place after the fibrillating milling.

Known blades in pulpers have edges of a few millimetres radius. These blades act as impact discs. They move the biomass inside the pulper as pulper drivers. There is no or only an insignificant amount of cutting. In contrast to this, for the method according to the invention, a high-consistency pulper with a spiral is proposed, in which the spiral has blades with an edges having a radius of less than 1 mm.

The present invention is based on the finding that it is expedient to use blades having a particularly sharp cutting edge in a high-consistency pulper. Sharp blades such as trimming knives or other sharp blades can be used as the cutting edges.

Two method schemata for preparing biomass are shown in the drawing and are described in more detail below.

FIG. 1 schematically shows a method with a bladed pulper and a pulper ball mill and

FIG. 2 schematically shows a method with a bladed pulper and two pulper ball mills.

The method shown in FIG. 1 is particularly suitable for green waste such as grass. This method is very advantageous, as the majority of the cellulose fibres which can be used for paper production can be exposed with it.

In the method schema T shown in FIG. 1, the first method step 2 is a dry preparation step. To this end, a rapidly rotating blade 3 is provided, which comminutes the green waste conveyed on the belt 4 like a lawnmower.

This is followed by a dry screening step 5, to which the oversize material 6 is fed back. Periodically occurring biomass in the form of wood chips 7 is disposed of by means of the trolley 8 and for example fed to a combined heat and power plant.

The undersize material 9 is fed to the high-consistency pulper 10 and treated there according to the kappa effect. The supplied undersize material 9 is cut using a bladed spiral 11 and the cut undersize material 12 is removed underneath a screen plate 13.

The bladed spiral 11 of the pulper 10 acting as the reactor is driven at high rotation speeds in order to achieve high cutting speeds.

A perforated plate with hole diameters of approx. 1 to 4 mm, for example 1.5 mm, is provided as the screen plate 13. The fibrous material is thereby extracted as cut undersize material 12. The pulper 10 is operated as a reactor in such a manner that the relatively long green waste are shortened to a length of approx. 5 to 6 mm which is expedient for paper production.

While the first main method step relates to cutting the fibres in the bladed reactor 10, the second main method step is fibrillating milling of the fibres in a continuously operated pulper ball mill 14. This pulper ball mill 14 has hole diameters of approximately 2 mm in the perforated plate 15, a spiral 16 and balls 17 which have approximately the density of plastic. During this fibrillating milling, the fibres are roughened in such a manner that they have a good connection to each other during later paper production.

This second process step in the pulper ball mill 14 is preferably operated in a two-stage manner. The fibrous material to be milled is milled with the addition or through-flow of relatively little water until the desired increase in strength is achieved. In a second step, the fibres are washed out of the ball fibre mixture using a relatively large amount of water.

In case there are particles in the washed-out fibrous material 18 which have an unsuitable size for paper production, post-sorting (classification) is carried out in a slotted sorter 19, which has slots of <0.3 mm in the sorting plate 20. The cleaned fibrous material 21 is then removed from the classifier 19, while the larger particles 22 are removed by means of the trolley 23.

The method shown in FIG. 1 with the two main method steps in the bladed pulper 10 and ball mill 14 can also be replaced by a three-stage method. This method step is shown in FIG. 2 without the pre- and post-treatment shown in FIG. 1.

In the method schema 30 shown in FIG. 2, a screening machine 34 is provided between the reactor 31 with the bladed spiral 32 and the pulper ball mill 33 in order to concentrate the fibrous portion 35 removed as undersize material from the reactor 31 and to free it from fine material 36 which would impede the milling process. The oversize material 37 of the concentrator 34 is fed to the pulper ball mill 33, which has lightweight balls such as plastic balls 38, as explained in the example of FIG. 1.

After fibrillating milling in the pulper ball mill 33, the milled fibrous material 8 exits the system for further use, in particular for paper production.

The oversize material 39 in the pulper 31 with the bladed spiral 32 is fed to a second pulper ball mill 40, which has heavier milling bodies 41, a spiral 42 and a screen plate 43. The oversize material 39 is subjected to a fibrillating milling process which shortens the fibres and at the same time opens up the woody constituents. The fibrous portion 44 then leaves the system.

A concentrator between the bladed pulper 10, 31 and the pulper ball mill 14, 33, 40 can be arranged at any point between these units. Owing to its washing properties, such a concentrator removes the constituents which are unsuitable for paper, such as ash, proteins, floury fine material, colloids etc. in order to separate them from the fibrous material in an early method step and feed them to another use. This includes the preparation of animal feed or else fermentation to produce biogas. When the balls in the pulper ball mills are selected, the diameters of the balls are 4 mm and above. If smaller balls of around 2 mm are used, too much fine material is produced, which impedes the process.

For the preparation of wood waste, wood-containing green waste or wood chips, the biomass is first pretreated in an autoclave. In this case the biomass is kept under pressure at approx. 120° C. in the autoclave for several hours, where necessary with the addition of water. In the process the wood becomes so soft that further treatment such as for green waste or together with green waste can be carried out. 

1. A method for preparing biomass, such as in particular wood-containing green waste, in which the biomass is treated in a continuously operated, bladed pulper and then the separated fibres are milled in a pulper ball mill.
 2. The method according to claim 1, wherein the consistency in the bladed pulper is from 10 to 20% dry content.
 3. The method according to claim 1, wherein the speed of the blade relative to the biomass in the bladed pulper is above 10 m/s.
 4. The method according to claim 1, wherein the separated fibres have a length between 1 mm and 5 mm.
 5. The method according to claim 1, wherein the biomass is processed dry before treatment in the continuously operated bladed pulper.
 6. The method according to claim 1, wherein the biomass is heated before treatment in the continuously operated bladed pulper.
 7. The method according to claim 6, wherein the biomass is heated under pressure.
 8. The method according to claim 6, wherein the biomass is kept hot for several hours.
 9. The method according to claim 1, wherein the separated fibres are concentrated on a screening machine and freed from fine material which impedes the milling process after it has been treated in the continuously operated bladed pulper.
 10. The method according to claim 1, wherein the separated fibres are milled in a fibrillating manner in the pulper ball mill.
 11. The method according to claim 1, wherein the separated fibres are milled in the pulper ball mill with lightweight balls which have approximately the density of plastic.
 12. The method according to claim 1, wherein the oversize material of the continuously operated bladed pulper is milled in a second pulper ball mill with heavy balls which have approximately the density of steel, stone or ceramic.
 13. The method according to claim 1, wherein a post-sorting process takes place after the fibrillating milling.
 14. A high-consistency pulper having a spiral, wherein the spiral has blades with a cutting edge having a radius of less than 1 mm. 